Below left, the border wall at San Pedro; at right, the barrier at Organ Pipe.

Then there are the Border Patrol trucks—thousands of them. The U.S. Fish and Wildlife Service reports nearly 8,000 miles of unauthorized roads and vehicle tracks, and that's just on the Cabeza Prieta National Wildlife Refuge. You might blame cross-border smuggling vehicles for the damage, but you'd be mostly wrong. The number of smuggler vehicles crossing these areas is almost nil thanks to the barriers, but damage from tire tracks, ruts and wildcat roads has increased dramatically.